Ink jet recording head

ABSTRACT

The object of the present invention is to provide a high-density ink-jet recording head provided with high resolution using thin film technique by preventing the characteristic of the displacement of a diaphragm from being deteriorated by the tension of the diaphragm, preventing the warp of a substrate from deteriorating the reliability and uniformity and preventing the looseness of the diaphragm from peeling a PZT film and from causing a failure of jetting. 
     The above ink-jet recording head is constituted so that the tension of the diaphragm in which a silicon oxide film ( 50 ) with negative tension and a lower electrode film ( 60 ) with positive tension are combined is substantially zero or negative and tension obtained by adding the tension of a piezoelectric film ( 70 ) with positive tension to the tension of the diaphragm is positive.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink-jet recording head used for anink-jet recording device. The present invention relates to an ink-jetrecording head provided with means for pressurizing an ink chamber usinga piezoelectric element as means for energizing ink.

2. Description of the Related Art

For prior art related to the present invention, technique disclosed inU.S. Pat. No. 5,265,315 and Japanese published unexamined patentapplication No. Hei5-504740 can be given.

In such prior art, after a silicon oxide film is formed on amonocrystalline silicon substrate by thermal oxidation so that the filmis 2500 Å thick, a lower electrode layer made of aluminum, nickel,chromium or platinum and others is formed so that the lower electrodefilm is 0.2 μm thick, next lead zirconate titanate (PZT) which is apiezoelectric substance is formed by sol-gel transformation so that itis 2 to 10 μm thick, further after an upper electrode film is laminated,and a through hole in the direction of the thickness of the siliconsubstrate to be an ink chamber is formed from the rear of the siliconsubstrate by etching.

To realize the enhancement of resolution and the speedup of printingrespectively required for a printer currently, the size of an inkchamber is required to be reduced and simultaneously, a large number ofink chambers are required to be arranged in high density. To obtainrequired characteristics, miniaturizing an ink chamber, a diaphragm anda piezoelectric film are required to be simultaneously thinned.

If the thickness of a diaphragm and a piezoelectric film is a few μm orless, a method of baking a piezoelectric film after a thin film issequentially laminated on a substrate and forming an ink chamberafterward is effective for their manufacturing method as described abovein relation to the prior art.

However, if a diaphragm and a piezoelectric film are formed according tothe above process and constitution, a lower electrode film tries tocontract remarkably in the heat treatment of a PZT film and largepositive residual stress is accumulated.

The tension by residual stress of the lower electrode film is tensileforce and is larger than the tension by residual stress of another film.Therefore, the tension of the diaphragm remarkably increases therigidity of the diaphragm as a drumhead strongly strained.

The effect of such tension of a diaphragm is not particularly a problemin a conventional type ink-jet recording head in which a diaphragm isformed so that it is 10 μm or thicker. The reason is as follows: For therigidity of a conventional type thick diaphragm, flexural rigiditydominates and is in proportion to the third power of the thickness ofthe diaphragm. In the meantime, the rigidity by the tension of thediaphragm is in proportion to the first power of the thickness.Therefore, as a diaphragm becomes thick, flexural rigidity rapidlybecomes large and the effect of the tension of the diaphragm relativelyrapidly becomes small.

There is a problem that as piezoelectric displacement when a PZT film isdriven operates upon the tension of a diaphragm, surplus energy isrequired and the efficiency of displacement for driving voltage isremarkably deteriorated.

Further, there is a problem that the tension of the diaphragm on asubstrate warps the substrate, a failure of joining occurs when thesubstrate is joined to another substrate and a yield is remarkablydeteriorated.

There is also a problem that even if joining is normally done,dispersion occurs in the tension of the diaphragm in the substrate, thecharacteristic of plural ink chambers becomes uneven and the quality ofprinting is deteriorated.

Conversely, there is a problem that if the tension of the diaphragm isthe tension of compression, the diaphragm is loosened or buckled and thejetting of an ink droplet is unstable. Further, there is a problem thatpeeling is caused in an interface between the lower electrode film andthe PZT film.

SUMMARY OF THE INVENTION

The present invention is made to solve these problems and the object isto provide a reliable ink-jet recording head provided with highresolution.

To achieve the above object, the present invention is characterized inthat in an ink-jet recording head provided with plural ink chambersincluded inside a substrate and respectively partitioned by side walls,a diaphragm which is formed on the surface of the substrate, which sealsone side of the ink chamber and at least the upper surface of which actsas a lower electrode and a piezoelectric active part provided with apiezoelectric film arranged on the diaphragm corresponding to the inkchamber and an upper electrode formed on the piezoelectric film, theabove diaphragm is constituted as a laminated film provided with atleast two layers of a layer with positive stress and a layer withnegative stress, the tension of the diaphragm is substantially zero ornegative because of the above stress of the diaphragm, and tensionobtained by adding the tension of the above piezoelectric film to thetension of the diaphragm is positive.

The present invention is also characterized in that in an ink-jetrecording head provided with plural ink chambers included inside asubstrate and respectively partitioned by side walls, a diaphragm whichis formed on the surface of the substrate, which seals one side of theink chamber and on the lower surface of which an upper electrode isprovided and a piezoelectric film arranged on the diaphragmcorresponding to the ink chamber and held between the lower electrodeand the upper electrode, the above diaphragm is constituted as alaminated film provided with at least two layers of a layer withpositive stress and a layer with negative stress, the tension of thediaphragm is substantially zero or negative because of the above stressand tension obtained by adding the respective tension of thepiezoelectric film and the upper electrode to the tension of thediaphragm is positive.

In a favorable embodiment, the above diaphragm may be also provided witha silicon oxide layer formed by oxidizing the surface of amonocrystalline silicon substrate and a metal layer to be the abovelower electrode laminated on the silicon oxide layer and plural inkchambers respectively partitioned by side walls may be also formedinside the above monocrystalline silicon substrate.

It is desirable that the metal layer to be the lower electrode is aplatinum layer formed on the silicon oxide layer directly or via anintermediate layer for example and relationship between the siliconoxide layer and the platinum layer is as follows:

(Thickness of lower electrode film)/(Thickness of silicon oxidefilm)≦0.5.

Further, the above diaphragm may be also provided with a thin film partthinner than the thickness of the diaphragm in a part corresponding tothe above piezoelectric active part in at least a part of an area alongthe periphery of the ink chamber around the piezoelectric active part.

The above diaphragm may be also provided with a silicon oxide layerformed by oxidizing the surface of a monocrystalline silicon substrateand a metal layer to be the lower electrode laminated the silicon oxidelayer and at least a part in the direction of the thickness of the lowerelectrode may be also removed in the above thin film part.

The above thin film part is formed on both sides in the direction of thewidth of the piezoelectric active part for example.

According to the present invention, the tension of the diaphragm is keptthe tension of zero or compression by combining positive stress andnegative stress, no tensile force of the diaphragm which remarkablydeteriorates the quantity of displacement when a PZT film is driven isgenerated and the warp of the substrate can be also simultaneouslyreduced. As positive tension (tensile force) is generated inside alaminated film when positive stress by the contraction of thepiezoelectric film is further combined, the looseness of the diaphragmand the peeling of the PZT film are inhibited.

According to the above present invention, the characteristic of thedisplacement of the diaphragm by the driving of a piezoelectric elementcan be prevented by the tension of members constituting the diaphragmfrom being deteriorated. Therefore, ability for jetting an ink dropletcan be sufficiently enhanced, keeping driving voltage low. Thedeterioration of the characteristic by joining and the deterioration ofa yield by a failure of joining can be reduced by reducing the quantityof the warp of the substrate until it is small enough. Further, as nolooseness is also caused on the diaphragm if the tension of thediaphragm is prevented from being tensile force, the jetting of an inkdroplet is prevented from being unstable and peeling is prevented frombeing caused in an interface between the lower electrode film and thePZT film, the performance of the recording head can be enhanced as muchas possible, securing uniformity and reliability and an ink-jetrecording head in high density provided with high resolution using thinfilm technique can be supplied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing an ink-jet recording headequivalent to a first embodiment of the present invention;

FIGS. 2(a) and 2(b) are sectional views showing the ink-jet recordinghead equivalent to the first embodiment of the present invention;

FIGS. 3(a) to 3(e) show a thin film manufacturing process in the firstembodiment of the present invention;

FIGS. 4(a) to 4(c) show the thin film manufacturing process in the firstembodiment of the present invention;

FIGS. 5(a) to 5(c) show the thin film manufacturing process in the firstembodiment of the present invention;

FIGS. 6(a) to 6(c) are sectional views showing the main part of anink-jet recording head equivalent to a second embodiment of the presentinvention;

FIG. 7 is a plan showing a transformed example of the second embodimentof the present invention; and

FIG. 8 is a plan showing another transformed example of the secondembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail based upon anembodiment below.

First Embodiment

FIG. 1 is an assembly perspective drawing showing an ink-jet recordinghead equivalent to an embodiment of the present invention and FIGS. 2show the sectional structure in the longitudinal direction andcross-sectional direction of one ink chamber in the ink-jet recordinghead.

As shown in FIGS. 2(a) and 2(b), a passage forming substrate 10 made ofa monocrystalline silicon substrate is provided with the surfaceorientation of (110) in this embodiment, normally a monocrystallinesilicon substrate approximately 150 to 300 μm thick is used, desirably amonocrystalline silicon substrate approximately 180 to 280 μm thick andpreferably approximately 220 μm thick is suitable. The reason is thatarray density can be enhanced, keeping the rigidity of a partitionbetween adjacent ink chambers.

One face of the passage forming substrate 10 is open and on the othersurface, a diaphragm is constituted by a silicon oxide film 50 made ofsilicon dioxide formed by thermal oxidation beforehand with thethickness of 1 to 2 μm and a lower electrode film 60. A piezoelectricfilm 70 narrower than the width of an ink chamber 12 is laminated on thediaphragm equivalent to a part of the ink chamber 12 and an upperelectrode film 80 is formed on the piezoelectric film 70.

In the meantime, on the side of the open face of the passage formingsubstrate 10, the ink chamber 12 partitioned by plural partitions 11 isformed at the same pitch in a row 13 by anisotropic etching as describedlater. Two rows 13 composed of ink chambers 12 are provided, and areservoir 14 arranged in the shape of a letter C so that the reservoirsurrounds the two rows of ink chambers in three directions and inksupply ports 15 each of which connects each ink chamber 12 and thereservoir 14 under fixed fluid resistance are formed around the two rowsof ink chambers 12. Each ink supply port 15 communicating with one endof each ink chamber 12 is formed so that each ink supply port isshallower than each ink chamber 12. That is, the ink supply port 15 isformed by etching the monocrystalline silicon substrate halfway in thedirection of the thickness (half etching). The above half etching isenabled by adjusting etching time.

A reference hole 30 for aligning the passage forming substrate 10 isrespectively formed at the diagonal two corners of the passage formingsubstrate 10.

A nozzle plate 18 through which nozzle apertures 17 each of whichcommunicates with the ink chamber 12 at the opposite end of the inkchamber 12 where the ink supply port is connected; and is fixed on theside of the open face of the passage forming substrate 10 via anadhesive, a thermic welding film or others. The nozzle plate 18 is aplate made of glass ceramics or rust-resistant steel and others with thethickness of 0.1 to 1 mm for example and the coefficient of linearthermal expansion of 2.5 to 4.5[×10⁻⁶/° C.] for example at 300° C. orless. The nozzle plate 18 covers one surface of the passage formingsubstrate 10 overall with one surface and also functions as areinforcing plate for protecting the passage forming substrate 10 fromimpact and external force. A reference hole 19 is formed through thenozzle plate 18 respectively in a position corresponding to thereference hole 30 of the passage forming substrate 10.

The size of the ink chamber 12 for applying pressure for jetting an inkdroplet to ink and the size of the nozzle aperture 17 for jetting an inkdroplet are optimized according to the quantity of a jetted ink droplet,jetting speed and jetting frequency. For example, if 360 ink dropletsare to be recorded per inch, nozzle apertures 17 a few tens μm indiameter are required to be formed precisely.

In the meantime, as described above, the lower electrode film 60 withthe thickness of approximately 0.5 μm for example, the piezoelectricfilm 70 with the thickness of approximately 1 μm for example and theupper electrode film 80 with the thickness of approximately 0.1 μm forexample are laminated on the silicon oxide film 50 on the reverse sideto the open face of the passage forming substrate 10 in a processdescribed later and constitute a piezoelectric element. As describedabove, a piezoelectric element is independently provided every inkchamber 12 in an area opposite to each ink chamber 12 on the siliconoxide film 50, in this embodiment, the lower electrode film 60 functionsas a common electrode for piezoelectric elements and the upper electrodefilm 80 functions as an individual electrode for each piezoelectricelement, however, these may be also inverted for convenience of adriving circuit and wiring and a piezoelectric active part provided withthe piezoelectric film 70 and the upper electrode film 80 is formedevery ink chamber 12.

In this embodiment, the length in the direction of the array of the inkchamber 12 is set to 75 μm, the length in the direction of the depth isset to 2 μm, and the length in the direction of the array of thepiezoelectric film 70 formed over the ink chamber 12 is set to 60 μm.Pitch between the ink chambers 12 in the direction of the array is setto 141 μm in case 180 nozzles are arranged per inch and 64 ink chambersare arranged in a row. That is, as the piezoelectric active partcomposed of the piezoelectric film 70 and the upper electrode film 80 islocated only over the ink chamber 12 and no piezoelectric film 70 isprovided in a part in which no ink chamber is provided in the directionof the array, the same quantity of displacement can be obtained at smallvoltage when voltage is applied and the diaphragm corresponding to theink chamber 12 is deformed.

Such passage forming substrate 10 and nozzle plate 18 are fixed into afixing member 20 provided with a concave portion for holding these.Reference holes 20 a are also formed in a position corresponding to thereference hole 30 of the passage forming substrate 10 in the fixingmember 20.

An insulating layer 90 provided with electric insulation is formed sothat it covers at least the periphery of the upper surface of each upperelectrode film 80 and the side of each piezoelectric film 70. It isdesirable that the insulating layer 90 is formed by material whichenables formation by a method of forming a film and reshaping byetching, for example silicon oxide, silicon nitride and organic materialand preferably photosensitive polyimide low in rigidity and excellent inelectric insulation.

Referring to FIGS. 3(a)-3(e) and 4(a)-4(c), a process in which thepiezoelectric film 70 and others are formed on the passage formingsubstrate 10 made of a monocrystalline silicon substrate will bedescribed below.

As shown in FIG. 3(a), first, a wafer 220 μm thick with the surfaceorientation of (110) to be the passage forming substrate 10 is thermallyoxidized at the temperature of approximately 1200° C. in wet and siliconoxide films 50 and 51 are formed on both sides of the passage formingsubstrate 10 at a time.

Next, as shown in FIG. 3(b), the lower electrode film 60 is formed bysputtering. For the material of the lower electrode film 60, platinum(Pt) and others are favorable. Because the piezoelectric film 70described later and formed by sputtering and sol-gel transformation isrequired to be baked and crystallized at the temperature ofapproximately 600 to 1000° C. in the atmosphere of the air or oxygenafter forming. That is, the material of the lower electrode film 60 isrequired to keep conductivity in such atmosphere of oxygen of hightemperature and particularly, if PZT is used for the material of thepiezoelectric film 70, it is desirable that the change of conductivityby the diffusion of PbO is small and Pt is favorable for the reason.

In this embodiment, titanium, titanium oxide and titanium aresequentially formed by a few tens Å between the silicon oxide film 51and the lower electrode film 60 as an intermediate layer 55 as shown inFIG. 3(e) for enhancing adhesion strength. The titanium layer, thetitanium oxide layer and the titanium layer which are the intermediatelayers and the lower electrode film 60 are sequentially formed by D.C.sputtering and the titanium oxide layer of them is formed by reactivesputtering in the atmosphere of oxygen of 10%.

Therefore, in this embodiment, the diaphragm is composed of the siliconoxide film 50, the intermediate layers and the lower electrode film 60.An intermediate layer is not necessarily required to be provided and thediaphragm may be also composed of only the silicon oxide film 50 and thelower electrode film 60.

Next, as shown in FIG. 3(c), the piezoelectric film 70 is formed.Sputtering may be also used for forming the piezoelectric film 70,however, in this embodiment, so-called sol-gel transformation in whichthe piezoelectric film 70 made of metallic oxide is obtained bytransforming so-called sol in which a metallic organic substance isdissolved and dispersed in a solvent to gel by applying and drying andfurther, baking at high temperature is used.

The material of the piezoelectric film 70 formed by sol-geltransformation is homogeneous sol obtained by adding polypropyleneglycol the average molecular weight of which is 400 to metallic oxide inthe sol by 30 percent by weight and stirring it sufficiently after leadacetate of 0.105 mole, zirconium acetylacetonate of 0.045 mole,magnesium acetate of 0.005 mole and acetic acid of 30 ml respectivelyheated up to 100° C. and dissolved are cooled up to room temperature,titanium tetraisopropoxid of 0.040 mole and pentaethoxyniobium of 0.010mole are dissolved and added in/to ethyl cellosolve of 50 ml andacetylacetone is added by 30 ml and stabilized. Sol processed on thelower electrode film 60 is applied by spin, is temporarily baked at thetemperature of 400° C., an amorphous porous gel thin film is formed andthe above application and temporary baking are repeated until thepiezoelectric film has required thickness. Next, pre-annealing is doneby heating the piezoelectric film up to 650° C. for five seconds in theatmosphere of oxygen using a rapid thermal annealing (RTA) method andkeeping it for one minute. Further, the piezoelectric film is annealedby heating it up to 900° C. in the atmosphere of oxygen using the RTAmethod and keeping it for one minute and a final PZT piezoelectric thinfilm is obtained. When the materials of the piezoelectric film obtainedas described above were measured, they showed excellent characteristicsthat the dielectric constant was 2000 and the coefficient of strain bypiezoelectricity d31 was −150 pC/N.

Next, as shown in FIG. 3(d), platinum (Pt) is formed so that it is 200 Åthick by D.C. sputtering and the upper electrode film 80 is formed. Thematerial of the upper electrode film 80 has only to be conductivematerial and many metals such as Al, Au and Ni in addition to Pt,conductive oxide and others may be used.

Next, as shown in FIGS. 4(a) to 4(c), the lower electrode film 60, thepiezoelectric film 70 and the upper electrode film 80 are patterned.

First, as shown in FIG. 4(a), a photoresist is formed on the siliconoxide film 51, an opening is provided, the silicon oxide film 51 ispatterned in the aqueous solution of hydrofluoric acid and ammoniumfluoride and the opening 51 a is formed. The direction of the depth ofthe opening 51 a, that is, a direction perpendicular to the surface ofthe drawing is equivalent to the direction of <112> of the passageforming substrate 10.

Next, as shown in FIG. 4(b), the lower electrode film 60, thepiezoelectric film 70 and the upper electrode film 80 are etchedtogether and the whole pattern of the lower electrode film 60 is formed.Next, as shown in FIG. 4(c), only the piezoelectric film 70 and theupper electrode film 80 are etched and the piezoelectric active part 320is patterned.

After the lower electrode film 60 and others are patterned as describedabove, it is desirable that an insulating layer 90 provided withelectric insulation is formed so that the insulating layer covers atleast the periphery of the upper surface of each upper electrode film 80and the respective sides of the piezoelectric film 70 and the lowerelectrode film 60 as shown in FIGS. 2(a) and 2(b).

A contact hole 90 a is formed in a part of the insulating film 90 whichcovers the upper surface of the part corresponding to one end of eachpiezoelectric active part 320. A lead electrode 100 one end of which isconnected to each upper electrode film 80 via the contact hole 90 a andthe other end of which is extended to a connecting terminal is formed.

FIGS. 5(a)-5(c) show a process for forming the above insulating layerand the above lead electrode.

First, as shown in FIG. 5(a), the insulating layer 90 is formed so thatit covers the periphery of the upper electrode film 80 and therespective sides of the piezoelectric film 70 and the lower electrodefilm 60. Negative photosensitive polyimide is used for the insulatinglayer 90 in this embodiment.

Next, as shown in FIG. 5(b), the contact hole 90 a is formed in a partcorresponding to the vicinity of the end on the side of the ink supplyport of each ink chamber 12 by patterning the insulating layer 90. Thecontact hole 90 a has only to be provided in a part corresponding to thepiezoelectric active part 320 and for example, may be also provided inthe center and at the end on the side of a nozzle.

Next, the lead electrode 100 is formed by patterning an electricconductor after the electric conductor such as Cr—Au is formed overall.

The process for forming films is described above. After the films areformed as described above, the passage forming substrate 10 isanisotropically etched from the opening 51 a of the silicon oxide film51 by dipping in the aqueous solution of potassium hydroxide of 80° C.as shown in FIG. 5(c), etching is continued until the silicon oxide film50 is exposed and the ink chamber 12 is formed.

In the above anisotropic etching, as the surface orientation of thepassage forming substrate 10 is (110) and further, the direction of thedepth of the opening 51 a is <112> as described above, the surfaceorientation of the side wall forming the side in the direction of thedepth of the ink chamber 12 can be (111).

As the ratio in etching speed of the surface (110) and the surface (111)of monocrystalline silicon is approximately 300 to 1 if the aqueoussolution of potassium hydroxide is used and a groove 220 μm deep whichis equivalent to the thickness of the passage forming substrate can beformed so that the width is approximately 1 μm by side etching, the inkchamber 12 can be precisely formed.

As for such an ink-jet recording head, multiple chips are simultaneouslyformed on one wafer by the above series of forming films and anisotropicetching and after the process is finished, the wafer is divided intoeach passage forming substrate 10 equivalent to one chip and shown inFIG. 1. The divided passage forming substrate 10 is sequentially bondedto the nozzle plate 18 and the fixing member 20 and integrated with themto be an ink-jet recording head.

In the ink-jet recording head constituted as described above, ink istaken in from an ink inlet 16 connected to external ink supply means notshown and after the inside from the reservoir 14 to the nozzle aperture17 is filled with ink, pressure in the ink chamber 12 is increased andan ink droplet is jetted from the nozzle aperture 17 by applying voltagebetween the lower electrode film 60 and the upper electrode film 80 viathe conductive pattern 100 according to a recording signal from anexternal driving circuit not shown and deforming the silicon oxide film50 and the piezoelectric film 70.

The tension of the silicon oxide films 50 and 51, the lower electrodefilm 60 and the piezoelectric film 70 in the above ink-jet recordinghead will be described below.

As the silicon oxide film is formed by thermal oxidation, it is expandedon the silicon substrate and negative stress is generated. That is, thesilicon oxide film receives compressive force from the silicon substrateand conversely, the silicon substrate receives tensile force from thesilicon oxide film. As the compressive tension of the silicon oxide filmequally acts on both sides of the silicon substrate, the siliconsubstrate is never warped.

In the meantime, the lower electrode film and the piezoelectric film arecontracted in a process of heat treatment at high temperature in whichhigh temperature lowers and have positive stress over the siliconsubstrate at ordinary temperature. That is, the lower electrode film andthe piezoelectric film receive tensile force from the silicon substrateand conversely, the silicon substrate receives compressive force fromthe lower electrode film and the piezoelectric film. As the siliconsubstrate is thick enough when it is compared with another film, thesilicon substrate is described below as an object on which tension acts.The silicon substrate in which films are laminated is warped by tensileforce which operates upon the lower electrode film and the piezoelectricfilm with the surface of the lower electrode film or the piezoelectricfilm concave.

The tension or the stress of each film is measured as follows:

The silicon substrate is warped by the tension, however, if the radiusof curvature of the warp at this time is R, relationship between theradius of curvature R and the tension T or the stress σ of the thin filmis expressed by the following relational expression.$\frac{1}{R} = {{\frac{6{d\left( {1 - v_{s}} \right)}}{E_{s}D^{2}}\sigma} = {\frac{6\left( {1 - v_{s}} \right)}{E_{s}D^{2}}T}}$

In the above expression, “d” denotes the thickness of the thin film, “D”denotes the thickness of the silicon substrate, “v_(s)” denotesPoisson's ratio of the silicon substrate and “E_(s)” denotes Young'smodulus of the silicon substrate.

As the elastic constant of silicon is anisotropic in measuring thequantity of a warp, a sample in the shape of a strip along specificcrystal orientation is used and in calculation, Young's modulus andPoisson's ratio in the direction are used.

The tension of the silicon oxide film 50 is obtained from the quantityof a warp after the silicon oxide film 51 on one surface of the siliconsubstrate 10 is removed by etching.

The tension of the piezoelectric film 70 is obtained from the change ofthe quantity of a warp before and after the piezoelectric film 70 isremoved by etching.

The tension of the lower electrode film 60 is obtained from the quantityof a warp after the piezoelectric film 70 is removed. At this time, thesilicon oxide film is required to be formed on both sides of the siliconsubstrate.

To obtain stress from the tension obtained as described above, Young'smodulus of each film is required. Young's modulus is required to bemeasured carefully so that stress has no effect. As in measurement usinga twin tong or measurement using a film the periphery of which is fixed,different values are measured because of tension, Young's modulus isobtained based upon the characteristics of a load and flexure using acantilever.

(First constitution of films)

Table 1 shows first constitution of films according to the presentinvention.

TABLE 1 Young's Thickness modulus Stress Tension (nm) (Pa) (Pa) (N/m)Silicon 1000 6 × 10¹⁰ −2.2 × 10⁸  −216 oxide film Platinum 500 1.5 ×10¹¹   3.9 × 10⁸ 195 lower electrode film PZT piezo- 1000 5 × 10¹⁰ 1.5 ×10⁸ 150 electric film

In the above constitution, (thickness of lower electrodefilm)/(thickness of silicon oxide film) is set to 0.5. The stress of thelower electrode film and the silicon oxide film slightly variesdepending upon the thickness of the respective films and the method ofheat treatment, however, the respective tension of the lower electrodefilm 60 and the silicon oxide film 50 can be approximately matched bysetting the film parameter to 0.5. Therefore, the tension of thediaphragm is substantially zero. The warped quantity of the substrate inthe direction of the array of ink chambers 12 is 3 μm in a range inwhich the ink chambers 12 are arranged and the diaphragm is concave. Inthis embodiment, the silicon substrate 10, the nozzle plate 18 andothers are bonded by an adhesive, however, no failure of bonding occursin the quantity of the warp. The characteristic of the displacement ofthe diaphragm after bonding is also unchanged.

The quantity of displacement when the voltage of 10 V is applied to apiezoelectric element according to the above constitution is 110 nm. Inthe meantime, the quantity of displacement when the voltage of 10 V isapplied to constitution in which the silicon oxide film 50 opposite tothe ink chamber 12 is removed by etching in the above constitution is 80nm. As a result of measuring the rigidity (compliance) of the diaphragm,the change of the rigidity before and after the silicon oxide film 50 isremoved is slight. Generally, when the silicon oxide film is removed,the flexural rigidity of the diaphragm is reduced and the quantity ofdisplacement by the application of voltage is expected to be increasedby the quantity. In this embodiment, as the tension and the thicknessare set so that the tension is large and the thickness is thin, strongtensile force operates upon the diaphragm because of the positivetension of the lower electrode film 60 if the silicon oxide film withnegative tension is removed and the tension sets off the deterioratedquantity of the flexural rigidity. The efficiency of the displacement ofthe diaphragm by the piezoelectric element can be remarkably enhanced byconstituting so that the tension of the diaphragm is substantially zeroor negative as in the above constitution.

(Second constitution of films)

Table 2 shows second constitution of films according to the presentinvention.

TABLE 2 Young's Thickness modulus Stress Tension (nm) (Pa) (Pa) (N/m)Silicon 1500 6 × 10¹⁰ −1.9 × 10⁸  −288 oxide film Platinum 400 1.5 ×10¹¹   3.9 × 10⁸ 156 lower electrode film PZT piezo- 1000 5 × 10¹⁰ 1.5 ×10⁸ 150 electric film

In the above constitution, (thickness of lower electrodefilm)/(thickness of silicon oxide film) is set to 0.27. As the tensionof the silicon oxide film is larger in an absolute value than thetension of the lower electrode film, negative tension operates as thediaphragm. When the tension of the PZT piezoelectric film is added tothe tension of the diaphragm, the above tension becomes positive tensionas a whole, the diaphragm is never loosened and an ink droplet can benormally and stably jetted. Even after an etching process for thesilicon substrate 10, no peeling occurs.

The warped quantity of the substrate in the direction of the array ofink chambers 12 is substantially zero though the diaphragm is slightlyconcave by 1 μm in a range in which the ink chambers are arranged and noproblem of bonding occurs.

The quantity of displacement when voltage of 10 V is applied to apiezoelectric element according to the above constitution is 120 nm andis increased by approximately 10%, compared with that in the firstconstitution. The rigidity (compliance) of the diaphragm is increased by10% (is reduced by 10%), compared with that in the first constitution.Therefore, strong pressure can be generated at low driving voltage inthe ink chamber and in total, the characteristics are enhanced more by20% than in the first constitution.

(Third constitution of films)

Table 3 shows third constitution of films according to the presentinvention.

TABLE 3 Young's Thickness modulus Stress Tension (nm) (Pa) (Pa) (N/m)Silicon 1500 6 × 10¹⁰ −1.9 × 10⁸  −288 oxide film Platinum 400 1.5 ×10¹¹   3.9 × 10⁸ 156 lower electrode film PZT piezo- 600 5 × 10¹⁰ 1.5 ×10⁸ 90 electric film

In the above constitution, the PZT piezoelectric film is thinned,compared with that in the second constitution. In the constitution, thenegative tension of the silicon oxide film is stronger than the positivetension of the lower electrode film and the PZT piezoelectric film andthe diaphragm is loosened. Though it may be difficult to verify theabove looseness by a microscope and others, the jetting of an inkdroplet becomes unstable and difference in the characteristic among theink chambers 12 is increased. The peeling of a film may occur in anetching process for the silicon substrate 10 and a yield isdeteriorated.

(Fourth constitution of films)

Table 4 shows fourth constitution of films according to the presentinvention.

TABLE 4 Young's Thickness modulus Stress Tension (nm) (Pa) (Pa) (N/m)Silicon 500 6 × 10¹⁰ −2.3 × 10⁸  −114 oxide film Platinum 500 1.5 ×10¹¹   3.9 × 10⁸ 195 lower electrode film PZT piezo- 1000 5 × 10¹⁰ 1.5 ×10⁸ 150 electric film

In the above constitution, the silicon oxide film is thinned, comparedwith that in the first constitution and (thickness of lower electrodefilm)/(thickness of silicon oxide film) is set to 1. As the tension ofthe silicon oxide film is smaller in an absolute value than the tensionof the lower electrode film, positive tension operates as the diaphragm.The warped quantity of the substrate in the direction of the array ofink chambers 12 is 9 μm in a range in which the ink chambers arearranged by the tension of the diaphragm and the diaphragm is concave.Because of the above warp, a partial failure of bonding occurs and ayield is deteriorated. As the quantity of a warp varies depending uponbonding, the tension of the diaphragm varies every ink chamber anddispersion in the quantity of the displacement and the rigidity isincreased. Therefore, the quantity of jetted ink varies in the ink-jetrecording head and the quality of printing is deteriorated.

In the above embodiment, the silicon oxide film and the platinum filmare combined, however, another combination is also allowed.

Generally, if a second element (oxygen is equivalent in the aboveembodiment) is doped into the surface of the substrate and a film isformed, negative stress is generated in the film. Therefore, the similareffect can be also obtained in a film formed by doping boron andnitrogen into the surface of the silicon substrate in addition to thesilicon oxide film.

A palladium film and a film including both palladium and platinum can begiven in addition to the platinum film.

In the above embodiment, as the tension of the upper electrode film 80is small enough, compared with the tension of another film, the effectis not considered, however, the tensile force of the upper electrodefilm 80 is increased by selecting the material, the thickness or aforming method of the upper electrode film 80, positive tension isobtained by adding the respective tension of the upper electrode film80, the piezoelectric film 70 and the diaphragm and the similar effectcan be obtained.

Second Embodiment

FIGS. 6(a) to 6(c) show a piezoelectric active part and a pressuregenerating chamber in an ink-jet recording head equivalent to a secondembodiment of the present invention.

This embodiment is the same as the first embodiment except that a lowerelectrode film removed part 350 from which the lower electrode film 60is removed is provided next to both sides in the direction of the widthof a piezoelectric active part 320 composed of a piezoelectric film 70and an upper electrode film 80.

The lower electrode film removed part 350 is formed by etching in theshape of a predetermined pattern after the upper electrode film 80 andthe piezoelectric film 70 are patterned. As shown in FIG. 6(a), in thisembodiment, a part in which the lower electrode film removed part 350 isprovided is a part called an arm of a diaphragm, a part opposite to thevicinity of the periphery along both sides in the direction of the widthof the ink chamber 12 and as shown in a section A—A in FIG. 6(b), thelower electrode film 60 on both sides of the piezoelectric active part320 is removed.

The quantity of the displacement generated by applying voltage to thepiezoelectric active part 320 can be increased by providing the lowerelectrode film removed part 350 as described above.

In this embodiment, the lower electrode film removed part 350 is formedby completely removing the lower electrode film 60, however, as shown inFIG. 6(c), a lower electrode film removed part 350A in which a part ofthe lower electrode film 60 is removed by half etching and others and athin film is left may be also formed.

The pattern of the lower electrode film removed part is not limited tothat in the above example and for example, as shown in FIG. 7, a lowerelectrode film removed part 350B may be also formed outside both ends ofthe piezoelectric active part 320 in the longitudinal direction.

Also, for example, as shown in FIG. 8, a lower electrode film removedpart 350C may be also provided in the shape of a letter U along theperiphery in three directions except one end of the pressure generatingchamber 12.

Other Embodiment

Each embodiment of the present invention is described above, however,the basic constitution of the ink-jet recording head is not limited tothe above constitution.

For example, in the above embodiments, the nozzle aperture 17 isprovided in a direction perpendicular to the surface of the passageforming substrate 10, however, a nozzle aperture 17 may be also formedso that it is formed on the end face of the passage forming substrate 10and ink is jetted in a direction parallel to the surface.

The example in which the insulating layer is provided between thepiezoelectric element and the lead electrode is described above,however, the present invention is not limited to this, for example, ananisotropic conductive film may be also thermically welded to each upperelectrode film without providing an insulating layer, the anisotropicconductive film may be also connected to a lead electrode and may bealso connected using various bonding technique such as wire bonding.

As described above, the present invention can be applied to an ink-jetrecording head with various structure unless the object is violated.

As described above, the ink-jet recording head according to the presentinvention can be favorably used for an ink-jet recording device forrecording a character and image information using ink on a recordingmedium such as paper, metal, resin and cloth,

Further, the ink-jet recording head according to the present inventionis optimum as a small-sized high-density ink-jet recording head in whichimproved characteristics are made the most of and which is used for asmall-sized ink-jet recording device provided with high performance.

What is claimed is:
 1. An ink jet recording head, comprising: plural inkchambers included inside a substrate and respectively partitioned byside walls; a diaphragm which is formed on a surface of said substrate,wherein said diaphragm seals one side of said ink chambers and at leastan upper surface of said diaphragm acts as a lower electrode; and apiezoelectric active part provided with a piezoelectric film arranged onsaid diaphragm corresponding to said ink chamber and an upper electrodeformed on said piezoelectric film wherein: said diaphragm is constitutedas a laminated film provided with at least two layers of a layer withpositive stress and a layer with negative stress; a tension of saiddiaphragm is one of: substantially zero; and negative; and a sum of atension of said piezoelectric film and the tension of said diaphragm ispositive.
 2. An ink-jet recording head, comprising: plural ink chambersincluded inside a substrate and respectively partitioned by side walls;a diaphragm which is formed on a surface of said substrate, wherein saiddiaphragm seals one side of said ink chambers and a lower electrode isprovided on an upper surface of said diaphragm; and a piezoelectric filmarranged on said diaphragm corresponding to said ink chamber and heldbetween said lower electrode and said upper electrode, wherein: saiddiaphragm is constituted as a laminated film provided with at least twolayers of a layer with positive stress and a layer with negative stress;a tension of said diaphragm is one of: substantially zero; and negative;and a sum of a tension of said piezoelectric film, said upper electrode,and said diaphragm is positive.
 3. An ink-jet recording head accordingto claim 1, wherein: said diaphragm is provided with a silicon oxidelayer formed by oxidizing the surface of a monocrystalline siliconsubstrate and a metallic layer to be said lower electrode laminated onsaid silicon oxide layer; and plural ink chambers respectivelypartitioned by side walls are formed inside said monocrystalline siliconsubstrate.
 4. An ink-jet recording head according to claim 3, wherein:said metallic layer to be said lower electrode is a platinum layerformed on said silicon oxide layer directly or via an intermediatelayer; and relationship between said silicon oxide layer and saidplatinum layer is as follows: (thickness of lower electrodefilm)/(thickness of silicon oxide film)≦0.5.
 5. An ink-jet recordinghead according to any of claims 1, 2, 3, 4, or 8, wherein: saiddiaphragm is provided with a thin film part thinner than said diaphragmin a part corresponding to said piezoelectric active part at least in apart of an area along the periphery of said ink chamber around saidpiezoelectric active part.
 6. An ink-jet recording head according toclaim 5, wherein: said diaphragm is provided with a silicon oxide layerformed by oxidizing the surface of a monocrystalline silicon substrateand a metallic layer to be said lower electrode laminated on saidsilicon oxide layer; and at least a part in the direction of thethickness of said lower electrode is removed in said thin film part. 7.An ink-jet recording head according to claim 5, wherein: said thin filmpart is formed on both sides in the direction of the width of saidpiezoelectric active part.
 8. An ink-jet recording head according toclaim 2 wherein: said diaphragm is provided with a silicon oxide layerformed by oxidizing the surface of a monocrystalline silicon substrateand a metallic layer to be said lower electrode laminated on saidsilicon oxide layer; and plural ink chambers respectively partitioned byside walls are formed inside said monocrystalline silicon substrate. 9.An ink-jet recording head according to claim 6, wherein: said thin filmpart is formed on both sides in the direction of the width of saidpiezoelectric active part.
 10. The ink-jet recording head according toclaim 1, further including a lower electrode film removed part formed byremoving a portion of said lower electrode film in a vicinity of saidpiezoelectric active part.
 11. The ink-jet recording head according toclaim 10, wherein said lower electrode film removed part is formed in aU-shape provided along the periphery of said piezoelectric active part.12. An ink-jet recording head according to claim 1, wherein saidpiezoelectric film is narrower than a width of said ink chamber.
 13. Anink-jet recording head according to claim 2, wherein said piezoelectricfilm is narrower than a width of said ink chamber.
 14. An ink-jetrecording head according to claim 1, further including an insulatinglayer formed so that said insulating layer covers at least a peripheryof an upper surface of said upper electrode film and a side of saidpiezoelectric film.
 15. An ink-jet recording head according to claim 2,further including an insulating layer formed so that said insulatinglayer covers at least a periphery of an upper surface of said upperelectrode film and a side of said piezoelectric film.
 16. An ink-jetrecording head according to claim 14, wherein said insulating layer isprovided with electric insulation.
 17. An ink-jet recording headaccording to claim 15, wherein said insulating layer is provided withelectric insulation.
 18. An ink-jet recording head according to claim14, wherein said insulating layer is formed by a method of forming afilm and reshaping said film by an etching process.
 19. An ink-jetrecording head according to claim 15, wherein said insulating layer isformed by a method of forming a film and reshaping said film by anetching process.